On the dynamic behavior of a simple beam the influences of the velocities and distance of two moving masses have been studied by numerical method. The instant amplitude of a simple beam is calculated and analyzed for each position of the moving masses represented by the time functions. As increasing the velocties of two moving masses on the simple beam, the amplitude of the transverse vibration of the simple beam is decreased and the frequency of the transverse vibration of the simple beam is increased. As the distance between two moving masses increase, the transverse displacement of the simple beam is decrease. The simple beam is very stable in second mode at $ar{a}=0.5$ and in third mode at $ar{a}=0.3$.